Fluorocarbon elastomers (as classified as FKM elastomers by the American Society of Test Methods (ASTM)) are an important class of industrial polymers due to their unique inherent properties. They are especially known to retain their elongation and tensile strength properties under extremely harsh chemical and thermal conditions. Fluorocarbon elastomers find use as sealing O-rings, molded goods, and extruded articles where the resulting fluorocarbon elastomer based articles are used in high temperature applications, and/or in applications where the article is exposed to harsh chemical environments. In particular, fluorocarbon elastomers are commonly used to make automotive components such as engine oil seals, fuel hoses, various O-rings, drive train seals, and other components that must maintain their properties while in contact with the operating conditions of combustion engines. However, the expense of fluorocarbon elastomers limits their use in many applications, while in other instances, current fluorocarbon elastomers lack certain physical property attributes, such as low temperature flex or modulus, high abrasion resistance, and low durometer or lack solvent resistance, such as to ketones and esters.
There have been relatively few successful attempts to provide modified fluorocarbon elastomers by the addition of, or combination with, other less expensive hydrocarbon or siloxane based polymers. Stable uniform mixtures are difficult to obtain due to the incompatibility of fluorocarbons with these polymers. Moreover, blends must be co-crosslinkable. Some examples to provide fluorocarbon and silicone elastomer compositions include U.S. Pat. No. 4,942,202, 4,985,483, 5,010,137, 5,171,787 and 5,350,804.
U.S. Pat. No. 4,942,202 teaches a rubber composition and vulcanized rubber products, which included fluorocarbons. The '202 compositions are prepared by reacting an organic peroxide, under shear deformation, with (I) a silicone rubber, (II) a saturated elastomer that fails to react with an organic peroxide when it is used alone, and (III) another elastomer that is co-crosslinkable with the silicone rubber in the presence of an organic peroxide. The other elastomer (III) is also co-crosslinkable or highly miscible with component (II).
U.S. Pat. No. 4,985,483 discloses fluororubber compositions containing dispersed particles of cured silicone material. The '483 compositions contain from 0.1 to 30 weight parts per 100 weight parts of a fluorocarbon of a finely divided cured silicone material in the form of a rubber, gel, or resin. The silicone material is first cured before mixing with the fluorocarbon. Preferably the silicone material used in the '483 patent is prepared using aqueous dispersion techniques described in U.S. Pat. No. 4,742,142, which provides silicone rubber particles having a size of less than 100 micrometers.
U.S. Pat. No. 5,010,137 teaches rubber compositions, which include fluorocarbons, and oil seals and rubber hoses obtained therefrom. The '137 compositions are obtained by compounding a polyorganohydrogensiloxane and a group VIII transition metal compound with a rubber-forming polymer comprising (I) a vinyl containing polyorganosiloxane and (II) an organic rubber, and subjecting the resulting compound to hydrosilylation while effecting shear deformation.
U.S. Pat. No. 5,171,787 teaches silicone-based composite rubber compositions, including fluorocarbons, and uses thereof. The '787 compositions are prepared by compounding a (A) rubber forming polymer comprising a polyorganosiloxane and an organic rubber, (B) a silicon compound having at least two hydrolyzable groups per molecule, and (C) a heavy metal compound, amine, or quaternary ammonium salt which catalyzes the hydrolysis and condensation reaction; and allowing the resulting formulation to undergo hydrolysis and condensation reactions while the formulation is kept from being deformed by shearing; and a crosslinking agent subsequently added followed by crosslinking of said organic rubber.
U.S. Pat. No. 5,350,804 teaches a composite rubber composition which comprises (a) an organic rubbery elastomer composition having a Mooney viscosity of at least 70 at 100° C. forming the matrix phase of the composite rubber composition; and (b) cured silicone rubber as a dispersed phase in the matrix phase.
While these patents provide advances in the field, a need still exists to specifically modify fluorocarbon elastomers in an efficient manner to provide lower cost high performance elastomeric systems, while maintaining the inherent physical properties of fluorocarbons. In particular, there is a need to provide lower cost fluorocarbon elastomer compositions for use in various applications where high and or low temperature properties are required as well as resistance to fuels, oils, exhaust gases, or chemicals.
The present invention provides fluorocarbon elastomeric compositions based on the incorporation of silicones with fluorocarbons using a new mixing process then a static vulcanization process. These new processes provide compositions having significant quantities of a silicone rubber based composition incorporated into a fluorocarbon elastomer. However, the resulting cured fluorocarbon rubber composition prepared from the fluorocarbon elastomeric compositions of the present invention, maintain many of the desirable fluorocarbon physical property attributes, such as fuel impermeability.